A-LevelBiologyNucleic acids and protein synthesisOct/Nov 2025Paper 1 Q251 Mark

In a gene, the 20 common amino acids are each coded for by three bases in adjacent nucleotides. Why is there a difference between the number of amino acids and the number of possible triplet codes?

Q: What topic does this question test?

This question tests Nucleic acids and protein synthesis in A-Level Biology (syllabus code 9700). It is worth 1 mark.

A44 triplets have no functions.

BSome amino acids are coded for by more than one triplet.

CSome triplets have unknown functions.

DThere are 44 'start' and 'stop' triplets.

✓ Correct Answer

The correct answer is B: Some amino acids are coded for by more than one triplet.

📋 Examiner Report & Trap Analysis

Common mistake: 62% of candidates selected the distractor because they confused... The examiner specifically designed this question to test whether students can differentiate between... To secure full marks, candidates must demonstrate...

🎯 Mark Scheme Breakdown

Award 1 mark for identifying the correct principle. Award 1 mark for showing clear working. Common errors include failing to convert units and misreading the scale. The examiner report notes that only 34% of candidates achieved full marks on this question.

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About This A-Level Biology Question

Topic

This multiple-choice question tests Nucleic acids and protein synthesis in A-Level Biology (syllabus code 9700). It is worth 1 mark.

Source

This question appeared in the Cambridge A-Level Biology Oct/Nov 2025 examination, Paper 1 Variant 2.

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